1. Field of the Invention
The present invention relates to a diagnosis method for state-of-health (SOH) of batteries. Particularly, the present invention relates to the diagnosis method for SOH of batteries by measuring discharge voltages and currents of a battery unit within a predetermined period of time. More particularly, the present invention relates to the diagnosis method for SOH of the battery unit by utilizing changes of discharge voltages and currents of the battery unit.
2. Description of the Related Art
Computer appliances currently require high-quality power sources. Power failure or unstable power supplies can cause serious damages of various equipment, such as workstations, medical equipment, industrial machineries etc. In order to satisfy demands of stable power or to ensure uninterrupted power, a high-quality power source such as a battery unit is used to supply electric power (as a backup power source) in the event of power failure. In addition to this, in the past, batteries as power storage devices were employed to store electric energy for use in some appliances such as communication devices, emergency illuminating devices, and power-driven vehicles etc. However, in long-term use, batteries have the problem of deterioration or aging (i.e. close to the end of its charge/discharge cycle life). In this situation, batteries are no longer supplying a reliable power. Hence, there is a need for evaluating the SOH of batteries.
There are several reasons that may result in the deterioration or aging of the lead-acid battery, including corrosion of plates of battery electrodes, deterioration of active materials of electrodes, irreversible active materials, occurrence of short circuits and loss liquid. Additionally, there exists abnormal deformation in a discharge profile during discharging the battery if the battery has aged in long-term use.
Several approaches have been currently used to determine the condition of a battery. In general, diagnosis methods for SOH of batteries include the following: analyzing an available charge capacity of a battery; analyzing discharge voltages of a battery (known as “coup de fout” method); analyzing an impedance characteristic of a battery; analyzing discharging and charging states of a battery; and analyzing method of using artificial intelligence (AI) etc. However, these methods are not accurate or reliable diagnosis methods for SOH of lead-acid batteries.
There are many factors, including charging process and method, discharging current, storage temperature and initial battery's state, which can affect the charge capacity of the battery. In addition, there is a need for employing a number of precision instruments in a method either of analyzing battery's discharge voltages or analyzing a battery's impedance characteristic. Alternatively, an analyzing procedure is sophisticated in a method of analyzing battery's discharging and charging states or an analyzing method of using artificial intelligence.
A conventional method for diagnosis of the SOH of batteries, described in U.S. Pat. No. 6,668,247, utilizes two separate necessary requirements of detecting an impedance characteristic of the battery and counting the number of complete charge/discharge cycles of the battery. The data of the impedance characteristic and the number of complete charge/discharge cycles of the battery must be calculated in a fuzzy logic system in such a way that relationships among the impedance characteristic, the number of complete charge/discharge cycles and the state of health of the battery is used to train the fuzzy logic system. However, there is a need for a number of hardware equipment (including a signal generator, an impedance measuring device and a voltage/current measuring device for example) equipped for processing such a diagnosis method of the battery's SOH. Also, there is another need for training the fuzzy logic system which has been already used to enter a great deal of data of the impedance characteristic and the number of complete charge/discharge cycles of the battery. Consequently, the fuzzy logic system can be used to determine the SOH of batteries.
As mentioned above, the diagnosis method for the SOH of batteries disclosed in U.S. Pat. No. 6,668,247 requires a highly sophisticated system. Generally, a battery has a very small value of impedance within a range of about several milliohms to about ten more milliohms for use in practicing the diagnosis method. Accordingly, the signal generator and the impedance measuring device must be precise to measure such a small value of impedance of the battery. Inevitably, there is a need of regular adjustment of precision instruments for measuring such a small value of impedance of the battery, or errors of the precision instruments may be continuously enlarged in repeatedly using them to practice the diagnosis method. In addition, many different brands or types of batteries, which have been widely used, have different characteristics. Accordingly, the fuzzy logic system must be separately trained to meet the battery characteristics of different brands or types. However, there is a need for retraining the fuzzy logic system in diagnosis of the SOH of batteries if the selected brand of battery cannot meet the battery characteristic previously designated in the fuzzy logic system. Disadvantageously, the entire procedure is highly sophisticated in practicing such a diagnosis method.
Another conventional method for determining SOH of batteries, described in U.S. Pat. No. 6,362,601, utilizes a degree of degradation of a battery plate (electrode plate) or decrease in capacity per time versus temperature in determining a float voltage of a float charging system. In this diagnosis method, a voltage of a fully charged battery at the end of the restoration charge is utilized to determine the SOH of the battery. The battery is assumed to be healthy if the determined voltage of the battery falls within a healthy state limit window at the end of the restoration charge.
As mentioned above, the diagnosis method for the SOH of batteries disclosed in U.S. Pat. No. 6,362,601 utilizes curves illustrating a battery electrode in relation to self-discharge, deep discharge and battery ageing in indicating a degree of degradation of the battery. Due to different battery characteristics of various brands or types, there is a need of showing various curves of the battery electrode in relation to self-discharge, deep discharge and battery ageing. Accordingly, the entire procedure of the diagnosis method must be repeatedly retrained and restarted. However, this diagnosis method will be only suitable for use in a float charge system and cannot meet the need of an indication for the SOH of the batteries.
As is described in greater detail below, the present invention intends to provide a diagnosis method for SOH of batteries by measuring discharge voltages and currents of a battery unit within a predetermined period of time. Changes of the discharge voltages and currents are used to indicate a degree of SOH of the battery in such a way as to directly determine the SOH of the battery, and thus to simplify the diagnosis method for the SOH of the batteries.